Accounting for Displacement: Drivers, Ports, and Electronics

When a speaker design software (like WinISD) tells you your ideal cabinet volume is 45 Liters, it is talking about Net Internal Volume—the actual amount of empty air inside the box.

A common mistake beginners make is building a box with exactly 45 Liters of internal space, and then stuffing a massive subwoofer, a heavy port tube, and a plate amplifier inside it. By the time everything is installed, the actual air volume might only be 38 Liters. This drastically shifts the tuning frequency and chokes the low-end response!

What needs to be displaced?

• The Speaker Driver: The magnet and basket sit inside the box and displace air. A massive 18" subwoofer can displace upwards of 6 to 8 Liters all on its own!
• Ports and Vents: The physical wood or plastic used to make the port tube takes up space.
• Electronics: Plate amplifiers or internal crossovers reduce the available air volume.
• Internal Bracing: Any wooden braces you add to prevent resonance must be accounted for.

How to solve this easily

Calculating the volume of a complex speaker magnet by hand is difficult. That is why Volume App includes dedicated tools to make this effortless:

• Driver Displacement Tool: Simply input the physical dimensions of your driver (magnet width, depth, etc.) and we calculate the exact volume it displaces.
• Additional Displacement Field: Have a plate amplifier that takes up 2 Liters? Just type "2" into the Additional Displacement field.

Once you enter these values, Volume App will automatically increase the physical dimensions of your box so that your Net Internal Volume remains perfectly matched to your target!